1. Field of the Invention
The present invention relates to a manufacture method of tubular member and the tubular member manufactured by this method. Particularly, the invention relates to a manufacture method of tubular member having a tube expansion portion and the tubular member manufactured by the method.
2. Description of Related Art
A tubular member having a tube expansion portion at one end thereof (see, for example, Japanese Patent Application Publication No. 11-179453 (JP 11-179453 A)) can be manufactured by a method which includes, for example, a sheet rolling step to roll a flat sheet subject matter into a tubular configuration and a tube expanding step to expand the one end of the tubular subject matter. In this case, the sheet rolling step can obtain a tubular subject matter free from clearance at a butt connection by U-O bending the flat sheet subject matter using a U-bending die followed by an O-bending die. The tube expanding step may encounter a problem that the one end of the tubular subject matter is circumferentially drawn during the shape forming and the tubular subject matter is opened at the butt connection. It is therefore a conventional practice, for example, to weld bond the butt connection of the tubular subject matter formed by the sheet rolling step although it is unnecessary for the butt connection to be weld bonded to ensure a function of this part. This results in the increased number of steps which leads to reduced productivity as well as to increased manufacture costs.